The invention relates to a flat tube for heat exchangers with wide and narrow sides and an inner insert and with an introduction bevel in order to facilitate introduction of the inner insert. The invention also relates to a method (and installation) for producing flat tubes for heat exchangers.
The heat exchanger described in DE 199 27 607 A1 has flat tubes. In said publication, the known heat exchanger has been embodied specifically as a charge air cooler and therefore consists of aluminum sheets. The ends of the flat tubes were widened, the widened ends tightly abutting one another in a stack of flat tubes. The mutually abutting, end-side widenings also produce, in an advantageous manner between the flat tubes, channels through which a coolant can flow. Accordingly, the publication makes provision to dispense with the use of tube bottoms. The widenings of the flat tube ends are directly connected and an air box is arranged around the end-side circumference of the stack. The widenings have the positive side effect that the introduction of the inner inserts into the flat tubes is easier to bring about, as the widenings serve as introduction bevels. Nevertheless, the production of the flat tubes provided with the widenings is regarded as being very costly. In addition, soldering-related problems arise both in the tight connection of the widenings of the flat tube ends to one another and in the connection of the box to the aforementioned circumference of the stack of flat tubes. Furthermore, widenings often lead to a certain reduction in wall thickness, associated with the risk of the wall becoming torn down. It is therefore not possible to use such low wall or metal sheet thicknesses as would actually be desirable for reasons of weight and cost.
In other known solutions which dispense with the widening of the flat tube ends or with introduction bevels, the flat tube is usually continuously produced from the band on a rolling train or the like and cut to length. The flat tube is then deformed in the resilient region, that is to say brought in the direction of a slightly elliptical cross section, in order to facilitate the introduction of the inner insert. Owing to the later soldering, the tolerances of the inner inserts and the flat tubes have to be very close to one another; this compounds the difficulties. Such solutions are often also not quality-responsive, because the wall of the flat tubes does not automatically nestle snug against the inner inserts again after the inner inserts have been inserted. In order to achieve quality-responsive solderings, the wall has to be pressed flat against the inner inserts, wherein the narrow sides of the flat tubes can be deformed in an undefined manner, leading later to further problems when connecting the flat tube ends in openings of a tube bottom by soldering.
Possibly the most perfect known method for producing flat tubes with inner inserts from band material is distinguished in that both the flat tube and the inner insert are produced from endless bands on a rolling train or the like. In this case, over the course of the reshaping of the band into the flat tube shape, the inner insert, which has already been reshaped, is threaded into the flat tube and the reshaping of the flat tube is concluded. This method thus dispenses with the introduction of individual inner inserts into individual flat tubes altogether. However, it does present a few difficulties in the clean separating-off of individual flat tubes along with the inner insert from the endless flat tube. The enormous investment costs for implementing this method make it uneconomical when demand does not allow extensive large-scale production of flat tubes of equal dimensions. As an example of this known method, reference may be made to JP 05-115934 A.
Finally, for the production of flat tubes for heat exchangers, it is also known to punch out blanks, to reshape the blanks into the flat tube and to weld them in a longitudinal seam (see DE 196 45 928 A). The inner inserts can also be introduced into flat tubes produced in this way; however, this is associated with the above-described difficulties.